Disclaimer: If you do not have your SHSH blobs backed up for your AppleTV at 4.1 I HIGHLY advise avoiding any upgrading whatsoever, tethered or not, until a real proper jailbreak is available.

If you don’t understand the above GO BACK NOW, do NOT attempt the following.

Made it this far? Another warning: If you aren’t a developer or someone trying to tweak iOS 4.2.1 the following jailbreak is STRONGLY discouraged. Booting tethered on the AppleTV is an easy process, but it is still a PITA that a casual user would probably not have the desire to put up with.

Read the ENTIRE documentation at least once before running through the process.

You will need a computer that is close enough to your AppleTV that it can be plugged into USB, power and HDMI without any major movement of the AppleTV itself), if you don’t meet this requirement the following is impossible, unless your microUSB cable is REALLY long.

4. Run PwnageTool on the 4.2.1 ipsw (if you don’t know how to do this, again you REALLY shouldn’t be here) saving into the ~/Desktop/tethered folder with the default name PwnageTool gives it (AppleTV2,1_4.2.1_8C154_Custom_Restore.ipsw

6. Restore the AppleTV to the ~/Desktop/tethered/AppleTV2,1_4.2.1_8C154_Custom_Restore.ipsw firmware (your AppleTV SHOULD be in DFU mode after finishing up with PwnageTool)

NOTE: Do not install any packages through cydia in expert mode, this produced very unpredictable results.

7. Unplug and then replug the USB, after the AppleTV has finished started up (will be blinking steadily), plug in the power cable

8. Run the following commands in terminal:

cd ~/desktop/tethered

./tetheredboot -i iBSS.k66ap.RELEASE.dfu -k kernelcache.release.k66

NOTE: it will loop a complaint re: DFU mode, just ignore this, once you are finished getting in DFU mode tetheredboot will take over.

9. MANUALLY put the AppleTV in DFU (*DO NOT USE PWNAGETOOL*)

– Disconnect power cable and connect your Apple TV with your computer via microUSB – Now reboot your Apple TV by holding down Menu + Down buttons together for around 6 seconds. – After reboot, immediately hold Menu + Play until you see the message in iTunes saying that Apple TV in recovery mode is detected

10. if all went well, unplug USB and plug in HDMI and your AppleTV should be ready to go. You will need to repeat 7-9 every time you restart your AppleTV, this isn’t a convenient process by any stretch!

11. To get nitoTV installed (I couldn’t get the cydia, or custompackage sot work in PT)